Misfire and TPS adjustment issues
 

I have a couple of issues here that may or may not be related. Car is a stock 1997 LSI.

Issue #1: For some time now I've had issues with the torque converter locking and unlocking when cruising around 70 mph (randomly), and also a hard 1-2 shift (all the time). I've been suspecting the TPS may be bad.

Issue #2: I've got a major misfire at idle while cold that started Monday evening. Car runs fine during acceleration, cruising, and just general driving. But at idle, when cold, it misfired very badly. By the time the car was warm, the misfire had gone away.

I've checked the coils/plugs and they look great. Plugs were done this year with OEM plugs. I've also checked around all of the vacuum lines, grounds, and cleaned the MAF sensor just for the heck of it. Everything looked good. When I started the car up after taking the coils off and checking them, it misfired worse… so bad that the whole car was shaking. I triple checked the coils and everything I took off. It’s all back together properly.

I figured I'd check the TPS adjustment while I was in there since I've been suspecting it to be bad anyway due to issue #1. The document in the how-to section states that with the key on and throttle closed it should give .5 volts through the white wire on the plug. I measured mine and the volt meter shows 5.14 volts. My first thought was that I have my volt meter set incorrectly, but when I measure the battery on the same setting, it shows 12.2 volts. When I loosen the screws and adjust the position, the voltage doesn't change at all, but I get a loud buzzing sound that sounds like it's coming from the trans while I rotate it. Do I have a bad TPS, something else, or am I doing something wrong here? Could the TPS be the cause of my massive misfire/rough idle? Or completely unrelated?

Recent work that was done: Last weekend I changed the accessory belt and the front right axle. I took the black plastic intake off while doing the axle thinking it would be the easiest way to access the axle pin, but apparently it was unnecessary. My first thought after the misfire came was that bumped something when taking the intake off, but everything is connected properly and I cannot see anything out of place.

Edit to add: There is no CEL on.

Re: Misfire and TPS adjustment issues
 

Excuse the chopping but this bit is odd.:) 5.14V on the white wire is not right, you would get that voltage across the supply and the ground. But when you rotate it, it may not change your voltage, but it is changing the TPV at the TCU as you can hear the solenoids responding to the change.

The lock-up clutch acting like that is a sign, so no idea what it is but the TPS would be suspect.

Harvey.

Re: Misfire and TPS adjustment issues
 

Talk about odd... after reading your response I went out and moved the pin from the white wire to the red wire (the middle one). I was able to measure the voltage and adjust it to .50 volts exactly. The solenoids were constantly buzzing at .50 volts until I turned the car off and back on again. I assume this is normal?

So is my TPS wired incorrectly? It looks 100% original...

Also, I drove it around the block again and the misfire is still there. Not as bad at idle, but it's now hesitating severely during acceleration. The good (or maybe bad) news is that the CEL light finally popped on. I guess I'll be picking up an OBDII scanner tomorrow...

Re: Misfire and TPS adjustment issues
 

If you have an Auto Zone near you, you can borrow one free of charge.

Re: Misfire and TPS adjustment issues
 

Not any more at least in Ca some new law saying it was taking customers from repair shops by loaning the scanners out. So now they only sell them

Re: Misfire and TPS adjustment issues
 

Wow that sucks, but kinda funny. Around here you can go to any auto parts store and they will scan it for you, but I'm not sure if they let you take them home. I think it's time I just buy one, it would be nice to have...

Re: Misfire and TPS adjustment issues
 

The girl at Auto Zone said they can only scan 2000 or newer. Maybe she was lying cuz she did not know how or lazy , but did not get my 94 done.

Re: Misfire and TPS adjustment issues
 

Yes and no lol they can for 96 and newer as it would be obd2 system

Re: Misfire and TPS adjustment issues
 

Picked up a scanner today and checked the code.

"P0120 TPS/Pedal Position Sensor A Circuit Malfunction."

Of course, this didn't show up until after I adjusted the TPS... anybody got a used one laying around they want to get rid of?

Re: Misfire and TPS adjustment issues
 

just ohm test the tps it shoud read 5 ohms i believe.

Re: Misfire and TPS adjustment issues
 

When removed from the car, mine reads about 5.80 ohms with a fairly consistent change throughout the range of motion.

Re: Misfire and TPS adjustment issues
 

Checked it again this morning, moving it very, very slowly. It starts around 5.80, and when rotating it, it will reach about 5.4 ohms and then jump back up to 5.9, to 6.0, to 6.5, to 7.0, to 7.8, to 14+, and then back down to 5.0 and consistently smooth the rest of the rotation down to .05 ohms...

"Well there's yer problem!" :rolleyes:

Re: Misfire and TPS adjustment issues
 

Check the ground strap behind the dog bone on the bellhousing to see it its connected also.

Re: Misfire and TPS adjustment issues
 

That's the kind of thing I was hoping someone would come up with - something that I likely bumped when removing the intake. But nope. I just went and checked it and it looks good.

Replacement TPS on the way from Nate...

Re: Misfire and TPS adjustment issues
 

I installed the replacement TPS (used) today and still have issues, but they've changed slightly... :rolleyes: No CEL but now I have a high idle (1300 to 1500 rpm) in Park and Neutral, slight hesitation under very light throttle right off idle, and a random misfire at idle. But it's much better than it was before...

Car drives fine once you get past the slight stumble at take-off.

Also, the replacement TPS did not change the hard 1-2 shift. :rolleyes: